Electron camera



April 6, 1943. v s 2,315,621

ELECTRON CAMERA Filled Sept. 24, 1940 29 PHOTO SENSITIVE RECTANGULAR 0UTPU T AMP.

4/ III II PHO 7'0 SENS! TIVE CA THODE AAAAA /'N VE N TOR A T TORNEYPatented Apr. 6, 1943 ELECTRON CAMERA Herbert E. Ives, Montclair, N. J.,assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y.,a corporation of New York Application September 24, 1940, Serial No.358,064 16 Claims. (01. lie-7.2)

This application relates to electron discharge devicesand morespecifically to electron camera tubes used as television transmitters.

One well-known electron camera tube used as a television transmitter isknown as the dissector. In tubes of this general type an image of anobject is thrown upon a photoelectric cathode within the tube givingrise to a moving electron stream, the various elemental portions of acrosssection of which correspond respectively to the correspondingelemental areas of the object. By

means of suitable electromagnetic deflecting coils, this stream iscaused to move across a scanning aperture in such a way that eachelemental portion of the stream enters the aperture once during eachscanning interval. The electrons passing through the scanning aperturestrike an anode member, which usually is the first electrode of anelectron multiplier in the output circuit of which is connected a signalresistance through which passes the television image current resultingfrom the scanning.

The dissector tube can be used to scan a moving motion picture film insuccessive transverse lines, th movement of the film providing theslower of the two scanning movements. An obstacle to satisfactoryperformance is the presence of irregularity of sensitiveness of thephotoelectric surface on which the film line image is projected. Anirregularity in a photoelectric cathode will be more pronounced in aline scanning dissector than it will be in one employing scanning in twodirections as a spot irregularity in a linear cathode shows up as a linein the received picture.

It is an object of this invention to provide methods of and apparatusfor compensating for irregularities in the photoelectric surface of acathode in a dissector employed as a line scanning apparatus. v

In an embodiment of the invention, fully described .bei ow andillustrated in Fig. 1 cf the drawing, there is provided an arrangementin which a distorted line image from a continuously moving film isformed one. photosensitive cathode surface by means of a lenscombination which is slightly cylindrical about a horizontal axis. Theeffect of the cylindrical lens is to spread out th line image into abroad band covering a large number of granules or particles of thephotosensitive surface. A vertical magnification of from 5 to to 1 willgenerally be sufficient. A vertical slit is provided in the dissector toscan the electron stream from the cathode, instead of th squar apertureusually used, in

order to pick up simultaneously all of the electrons emitted from anelemental transverse strip of the band. In a modification, by localintense magnetic focusing of the electron stream, the usual squareaperture can be used. The effect of any irregularity sensitized spot ofthe photoelectric cathode is thus minimized by being averaged down inthe image current. V

In a second embodiment of the invention. shown in Fig. 2, a special slitaperture is not required, the essential feature of this arrangementbeing the oscillation of the image on the dissector cathode by opticalmeans and the following of these oscillations exactly by the use ofdeflecting magnetic sweeps which are not otherwise used in the linemethod of scanning. The optical device producing the oscillations can bea pair of prisms rotating in opposite directions or a fiat plateoscillating about an axis. The speed of oscillation of the image shouldnot be exactly in phase with the frame or lateral sweep frequency, thusavoiding the use of the same element of the dissector screen bysuccessive images.

The invention will be more readily understood by referring to thefollowing description, taken. in connection with th accompanying drawingforming a part thereof, in which:

Fig, 1 shows a television scanning system according to the invention; 7V

Fig. 2 shows a second embodiment of the invention; and

Fig. 3 is a top view of the optical means for producing movement of theimage on the photosensitive cathode of the dissector shown in the systemof Fig. 2 after this means has been rotated degrees from the po itionshown in Fi 2. 7

Referring more specifically to the drawing, Fig. 1 shows one system forcarrying out the principles of the invention. In the televisiontransmitter system shown in Fig. 1, a film l8 contains successive frameimages, the vertical scanning component of which is supplied by thecontinuous movement of the film over rollers 40 and ll while horizontalscanning is accomplished by the use of a dissector tube H adapted to beused as a line scanner.

An image of a portion of the object on the film I0 is formed by asuitable optical systemr represented by the source I2, and lenses l3 andV I4, upon a diaphragm is having a slit aperture l6 therein. The slit Itallows the image of a single line to pass therethrough, which slit imageis magnified in a vertical direction by the cylindrical optical system,comprising the convex lens the rectangular aperture or slit 2 l in thepick-up electrode 22 behind which is located a target anode 23 which isschematically shown in Fig. l as being connected directly to an outputresistance 24 but which is in the more usual practice connectedto thisresistance through an electron multiplier, the first electrode of whichis the target member 23. Such an electron multiplier arrangement is wellknown to those skilled in the art. The focusing is preferably done bymagnetic coils 25 acting in a manner well known to those skilled in theoperation of dissectortubes. These focusing coils receive their currentfrom a source 26 acting through variable resistance 21.

aeiaeai Fig. 2 shows another embodiment of the iri vention. In thisarrangement the portion to the left of line X-X is the same as that tothe left of the line X--X in Fig. 1 and operates in the same manner. Inthe arrangement of Fig. 2,

however, an image of the slit aperture is is moved up and down on thesurface of the photosensitive cathode 20 by means of a pair of op ticalprisms 42 and 43 rotating in opposite direc The electron image,corresponding to a distorted line image, is caused to move horizontallyacross the slit aperture 2| by means of sweep coilsducting coating 32 isconnected to an internal point of the source 30. The resistance 24-isconnected'in the input circuit. of an amplifier 3| the output of whichmay be connected by means of suitable wire or radio channels to areceiving station. The tube H is preferably, with the exception of thespecial rectangular aperture 2| and the omission of the vertical sweepcoils, of the type of tube well known to the art as the dissector.

In order to better understand the operation of the arrangement shown inFig. 1, consider that there is a small spot A falling within thedistorted line image IS on the photosensitive cathode 20. If this spothas a photoelectric irregularity this irregularity in the usualarrangement appears as a streak or line in the received picture assumingthat the dissector is used as a line scanner. By amplifying the slitimage It in one direction to form the distorted image I9, the spot A isa much smaller part of the total width of the image |9, and its effect(due to its irregularity of sensitiveness) is greatly minimized inasmuchas the elemental areas across the whole width |9 go into making up thesignal tions as shown in Fig. 3. Any suitable means may be used toprovide this motion. The light emerging from the prisms 42 and 43oscillates up and down between the boundary positions represented by thepoints B and D, Fig. 2, accordingto a sine wave relation. Thisoscillation is matched by the motion imparted to the electron image bythe magnetic field formed by the magnetic coils 44 receiving currentfrom a sine wave oscillator 45 of the same frequency as the oscillationof the line image between points B and D. By means of the magnetic coil44, the image'of every line between B and'D is brought to a focus at.the aperture 46 in the diaphragm 41. Unlike the aperture 2| used in thesystemof Fig. 1 the aperture 46 need be only a square as in the usualdissector. Horizontal deflection of the light image across the aperture46 is produced as in the case of Fig. l by means of sweep coils 28receiving current of saw-tooth wave form from sweep circuit 29. Theother portions of the dissector tube and its external circuit are thesame as in the system of Fig. 1. In Fig. 2, which is an elevation view,the prisms 42 and 43 are shown in a position which will deflect theimage to the line D while in Fig. 3, which is a top perspective view ofthe prisms after they have been rotated 90 degrees from the position ofFig.

,2, there would be no reflection of the beam as the two sides areparallel.

shown in Fig. 2, consider that a point C located between the points Band D is of irregular photo sensitivity. By means of the arrangementshown in this figure only once in ten or twenty lines will the electronsemitted from the spot C be focused upon the aperture 46 and thisirregularity will thus not be noticed. In all positions of the lineimage between B and D the field generated by the coil 44 deflects theelectron stream to a line at the height of the aperture 46 and the lineis moved horizontally across this aperture, that is, at right angles tothe plane of the drawing, by

. means of line scanning field formed by the coil which appears in theresistance 24 and in the output circuit representative of a singleelemental area of the object. The continuous movement of the film l0which is driven between the rollers 40 and 4| in a manner well known andthe horizontal movement of the electron image of the strip l9 across theslot 2| forms the other direction of scanning so that the image currentproduced in the resistance 24 is representative of a two-dimensionalsubject.

As a modification, the current supplied to the focusing magnetic coils25 may be adjusted so that the electron image of the wide or distortedline I9 maybe brought down to a small line: at

the plane of the aperture so that-the usual square of the same elementsof the dissector screen for successive images. This causes anyirregularities of a point such as the point C to be even furtherunnoticed. As a modification, the prisms may be replaced by a fiat plateoscillating about an axis.

As a modification of the optical systems in Figs. 1 and 2, a linearportion of the film may be imaged directly on the cathode 2|! byremoving the diaphragm I5 and placing the lens I! (or the prism 42 and43 of Fig. 3) close to the lens i4.

While the invention has been described above as applicable to thedissector type tube, it will be obvious that certain principles thereofare applicable as well to other types of transmitter tubes, for example,to a tube of the iconoscope type having a beam of a cross-section inwhich the longest dimension thereof is transverse to the scanningdirection anda photosensitive target upon which an image of a portion ofthe object, distorted in the direction transverse to scanning, isprojected.

Various other'modifications'maybe made in the embodiments describedabove without changing the invention, the scope of which is indicated bythe appended claims.

What is claimed. is:

1. An electron stream television camera for setting up image current incombination with means for directing light from single elemental stripsin succession of a continuously moving film or picture to be scanned andtherewith forming a distorted image field on the light receiving elementof said camera for each of said strips in succession thereby giving riseto a stream of photoelectrons, said image field having distortion due totoo great a dimension in ,a direction transverse to thelongitudinal'axis of said strip relative to the dimension in thedirection of said axis, and meanscomprising the electronstream of saidcamera for scanning in the direction corresponding to the lengths of'said strips and setting up image currents correspondingto-the tonevalues of said field in said direction by sweeping the photoelectronicstream repeatedly, once for each strip, in said direction.

2. An electron stream television camera of the dissector type forsetting upv image current in combination with means for directing lightfrom single elemental strips in succession of a continuously moving filmor picture to be scanned and therewith forminga distorted image field onthelight receiving element of said camera for each of said strips insuccession thereby giving rise to a stream of photoelectrons, said imagefield having distortion due to too great a-dimension in a directiontransverse to the longitudinal axis of said strip relative to thedimension in the direction of said axis, and means comprising theelectron stream of said camera for scanning in the directioncorresponding to the lengths of said strips and setting up imagecurrents corresponding to the tone values of said field in saiddirection by sweeping the photoelectronic stream repeatedly, once foreach strip, in said direction. 1 3. An electron stream television cameratube for setting up image current in combination with means fordirecting light from single elemental strips in succession of acontinuously moving film or picture to be scanned and therewithformstrips of said area, said strips being transverse- 4. In an electroncamera arrangement, a photoelectric surface within the electron camera,

'means for forming an image of a linear portion of an object on saidphotoelectric surface to cause the emission of a stream of electronstherefrom, the ratio of the height of the area of the photoelectricsurface which emits electrons when impinged upon by light from thelinear portion to the long dimension of said area.

5. vIn an electron camera arrangement, a photoelectric surface withinthe electron camera, means for forming an image of a linear portion ofan object on said photoelectric surface to cause the emission of astream of electrons therefrom, the ratio of the height of the area ofthe photoelectric surface which emits electrons. when impinged upon bylight from the linear portion of the object to the height of said linearportion being much greater than the ratio of the length of said area tothe length of said linear portion, a collecting" electrode for thephotoelectrons emitted from said surface, and a member having a slitaperture therein in front of said collecting electrode.

6. In an electron camera arrangement, a pho toelectric surface withinthe electron camera, means for forming an image of a linear portion ofan object on said photoelectric surface to cause the emission of astream of electrons therefrom, the ratio of the height of the area ofthe photoelectric surface which emits electrons when impinged upon bylight from the linear portion of the object to the height of said linearportion being much greater than the ratio of the length axis, and meanscomprising the electron stream of said camera for scanning in thedirection corresponding to the lengths of said strips and set-.

of said area to the length of said linear portion, a collectingelectrode for the electrons emitted from said surface, a member having aslit aperture therein in front of said collecting electrode,

and means for deflecting the stream of photo-' electrons emitted fromsaid surface across said slit in a direction perpendicular to the longdimension of said slit.

7. In an electron camera arrangement, a photoelectric surface within theelectron camera, optical means for forming a distorted image of a linearportion of an object on said photoelectric surface to cause the emissionof a stream of electrons therefrom, said image being enlarged in adirection transverse to the long dimension of said linear portion withrespect to the direction parallel to said long dimension, and means forcollecting the photoelectric emission from successive elemental stripsof the area of the photoelectric surface upon which the image isprojected, said strips being taken transverse to the long dimension ofsaid area. I

8. In an electron camera arrangement, a photoelectric surface within theelectron camera, optical means for forming in succession distortedimages of successive linear portions of a continuously moving object onsaid photoelectric surface to cause the emission of a st eam ofelectrons therefrom, said image being enlarged in a direction transverseto the long dimension of said linear portion with respect to thedirection parallel to said long dimension, a collecting electrode forattracting electrons emitted from said slit aperture therein in front ofsaid collectin electrode, the long dimension of said slit beintransverse to the long dimension of said linear portion.

9. In an electron camera arrangement, a photoelectric surface within theelectron camera".

optical means for forming an image ofa linear portion of an object onsaid photoelectric surface to cause the emission of astream ofphotoelectrons therefrom, said image being enlarged.

surface across said slit in a direction transverse to the long dimensionthereof.

10. In an electron camera arrangement, a photoelectric surface withinthe electron camera, means for forming an image of a linear portion ofan object on said photoelectric surface to causethe emission of a streamof photoelectrons therefrom, said means including apparatus for mov-"ing said image periodically in a direction transverse to the longdimension of the linear portion, an electrode for successivelycollecting electrons emitted by the various elemental portions of thephotoelectric surface struck by light from said object, and means fordeflecting the stream of photoelectrons in a direction transverse to thelong dimension of said linear portion of said object at a frequencywhich is the same as that of the movement of the image.

11. In an electron camera arrangement, a phophotoelectric surface, and amember having a image upon said cathode to form a corresponding movingelectrical image and deflecting said mov= ing electrical image at thesame frequency as the moving optical image and in such a phase that themoving line image is continuously fo cused at the same line, which linepasses through the aperture in front of the dlssector-pick-up electrode.

14. In an electron camera arrangement, a phoof an object on saidphotoelectric surface to cause toelectric surface within the electroncamera,

means for forming an image of a linear portion of an object on saidphotoelectric surface to cause the emission of a stream ofphotoelectrons therefrom, said means including apparatus for moving saidimage periodically in a direction transverse to the long dimension ofthe-linear portion, an electrode for successively collecting electronsemitted by the various elemental portions of the photoelectric surfacestruck by light from said object, and means for deflecting saidphotoelectron stream linearly with respect to time in a directionparallel to the long dimension of said linear portion.

12. The method of compensating for irreguthe emission of a streamof'photoelec'trons therefrom, said means including apparatus for movingsaid image periodically in a direction transverse to the long dimensionof the linear portion, an electrode for successively collectingphotoelectrons emitted by the various elemental portions of thephotoelectric surface struck 'by light from said object, means fordeflecting said photoelectron stream linearly with respect to time in adirection parallel to the long dimension of said linear portion, andmeans for deflecting the stream of photoelectrons in a directiontransverse to the long dimension of said linear portion of said objectat a frequency which is the same as that of the movementof said image.

15. In an electron camera arrangement, aphoe toelectric surface withinthe electron camera, means for forming an image of a linear portion onan object of said photoelectric surface to cause the emission of astream of photoelectrons there= from, said means including apparatus formoving said image periodically in a direction transverse to the longdimension of the linear portion,

an electrode for successively collecting-photoelectrons emitted by thevarious elemental portions of the photoelectric surface struckby lightfrom said object, means for deflecting said @photoelectron streamlinearly with respect to time in a direction parallel to the long.dimension of said linear portion, and means for deflecting the stream ofphotoelectrons in a direction transverse to the long dimension of saidlinear portion quency of the movement in the direction parallel to thelong dimension of the linear portionbeing different from the frequencyof movement in the direction transverse to the long dimension of thelinear portion.

16. In an electron camera arrangement, a pho- P toelectric surfacewithin the electron camera,

larities in a photoelectric surface of an electrode in an electroncamera tube used as a linear scanner of anobject, which comprisesforming a dis-.

said image to form an image current, the emlssion from the entire widthof an elemental portion giving rise to a signal representative of asingle elemental area of the object.

13. The method of compensating for irregularitiesin the photoelectricsurface of a dissector cathode, the dissector being used as a linearscanner, which comprises projecting a moving line means for forming animage of successive linear portions of a motion picture film onsaidphotoelectric surface to cause the emission of a stream ofphotoelectrons therefrom, said linear portion constituting a relativelysmall part of a frame of said motion picture film, said image formingimage but which frequency is dilferent from that at which completeframes of said motion picture film are scanned.

HERBERT E. IVES.

